Synthesis and Morphology Tuning of Gold Nanostructures and Their Applications

金納米結構的合成與形貌調控及其應用

Student thesis: Doctoral Thesis

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Award date8 Apr 2021

Abstract

Gold-based nanomaterials (AuNMs) have been enormously popular research objects for both fundamental and technical study due to their unique physiochemical, optoelectronic properties and a wide range of applications in the biomedical field. Notably, the optical and electronic properties of AuNMs can be finely tuned through modulating their sizes, shapes, and surface states. Therefore, the controllable synthesis of special morphologies with different sizes of AuNMs via simple and low-cost routes is an important research direction. This thesis mainly focuses on the synthesis and morphology tuning of two types of gold nanostructures: porous gold and flower-like gold, with their formation mechanisms unveiled and potential applications in the field of electronics.

Chapter 1 gives an introduction to the research background of the properties, synthesis methodologies and applications of porous gold and gold nanoparticles, respectively.

Chapter 2 then reports a convenient thiol compounds-mediated dealloying method for fabricating ultrafine nanoporous gold with feature size down to 4 nm (one of the smallest values reported to date) at an ambient air temperature. It is unraveled that the ultrafine ligament and pore sizes were mainly due to the lowered diffusion rate of the Au atoms at the alloy/electrolyte interface upon forming complexes with the thiol group in the etchant, which has been verified by the kinetics of nanopore formation and control experiments.

Chapter 3 explains how nanoporous gold was used to fabricate a continuous gold network via a novel, convenient, and low-cost synthesis methodology for the application of transparent conductive electrodes. The nanoporous gold produced by chemical dealloying was further heat-treated to achieve the coarsening of the Au ligament. Next, the coarsened porous gold was subjected to secondary etching to decrease its ligament size and increase its pore size. In addition, the pore and ligament size of the gold network can be conveniently tailored by controlling the experimental parameters, including the composition of the AuAg alloy, the thickness of the leaf, and the heating temperature. Ultimately, the obtained continuous gold network showed both excellent conductivity (sheet resistances down to 11.3 Ω/sq) and enhanced transmittance (approximately 51%).

In Chapter 4, flexible transparent conducting electrodes (FTCEs) based on gold mesh were fabricated through a simple new sputtering method. The resultant PET foil with Au mesh (PEAM) was found to exhibited high optical transparency (approximately 87%), good conductivity (sheet resistances down to 32 Ω/sq), and excellent mechanical flexibility (the conductivity dropped by only 4.9% after 450 bending cycles at a bending radius of 10 mm).

Finally, Chapter 5 reports the study of sunflower-like gold nanostructures fabricated by circularly polarized light-induced method in a novel photochemical system. The role of circularly polarized light in the method was revealed by monitoring the structural evolution of the gold nanostructure during the formation process as well as by comparison experiments involving tuning different types of irradiation light, including origin laser light, linearly polarized light, and circularly polarized light.